Microcombustors, microreformers, and methods involving combusting or reforming fluids

ABSTRACT

The invention describes combustors and steam reformers and methods of combustion and steam reforming. For example, integrated combustion reactors are described in which heat from combustion is transferred to an endothermic reaction. Thermally efficient reactors and methods of alcohol steam reforming are also described. Also described is an integrated combustor/reformer containing a methanation catalyst.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationNo. 10/008,363, filed Nov. 7, 2001, now U.S. Pat. No. 7,077,643.

This invention was made with Government support under DARPA contract #DABT63-99-C-0039. The Government has certain rights in this invention.

FIELD OF THE INVENTION

The invention relates to combustors and steam reformers, and methodsinvolving combusting or steam reforming.

BACKGROUND OF THE INVENTION

The ever-decreasing size of microelectronic devices and the rapiddevelopment of microelectromechanical systems (MEMS) have created agreat need for high energy density micropower supplies, for example, apower supply for microelectronic devices. Typically, conventionalbattery technology is used in these applications. However, currentbattery technology has a very low energy density, on the order of from0.035 to 0.350 kW_(e)-hr/kg. An alternative to batteries is to combine asmall fuel cell with a micro-hydrocarbon fuel processor. However, thusfar, it has not been possible to construct a very small, thermallyefficient fuel reformer. An additional problem is that many fuel cellsrequire hydrogen gas having very low levels of carbon monoxide (CO)contamination. Therefore, it is also desirable for a microreformer toproduce hydrogen that contains very little CO. Another problem is thatinstability in microcombustor operation can lead to partial vaporizationof the hydrocarbon fuel, if it is liquid, and to less than desiredconversion of the hydrocarbons to a hydrogen rich product stream due tothe intermittent lack of energy for the endothermic reactions.

Prior attempts to lower CO in a reformate mixture have included: a twostage methanation process conducted at two temperatures over a 2%Rh/alumina catalyst (Van Keulen, U.S. Pat. No. 6,207,307); passage ofthe reformate through a palladium membrane followed by methanation ofresidual CO over a catalyst such as Ru, Rh, Pd, Ir, Pt, Ni and Re (Somaet al., U.S. Pat. No. 5,612,012); passage of the reformate through ahydrogen selective membrane followed by methanation of residual CO(Edlund, U.S. Pat. No. 5,861,137); and heating a gas in the presence ofa water-gas shift catalyst to reduce the CO content to about 3000 partsper million (ppm), removing water, followed by reaction over Ru or Rh onalumina at below 250 C (Baker et al., U.S. Pat. No. 3,615,164).

Bohm et al. in U.S. Pat. No. 5,904,913 stated that methanol can bereformed at 220 to 280° C. over a Cu/ZnO on alumina catalyst. Bohm etal. reported that they had found that in their apparatus, for a methanolconversion above 98%, with a maximum reaction tube length of 160 cm, areaction temperature of at least 260° C. should be selected. Lowertemperatures would require longer reaction tube lengths. In theirapparatus, for a catalyst loading of 1.3 kg, a productivity of 8 Nm³H₂/hwas achieved, which required a minimum temperature of 280° C. for 100%methanol conversion. To lower CO, output from the reforming reactiontubes can be passed to a CO converter to methanate the CO over atitania/alumina/Ru/RuO_(x) catalyst with a Ru/RuO_(x) fraction ofbetween 2 to 4% at a maximum temperature of about 200° C.

The prior art processes for reforming hydrocarbons to produce hydrogensuitable for a fuel cell typically require multiple step operations inlarge and complex apparatus. Thus, there remains a need formicrocombustors and fuel reformers which have a very small size, steadyperformance, and operate at low temperature with low CO output whilemaintaining high efficiency levels.

SUMMARY OF THE INVENTION

The present invention provides microcombustors and microreformers whichcan be made with a very small size and which can operate at lowtemperature. The invention also provides devices utilizing the inventivemicrocombustors and/or microreformers instead of more conventionaldevices such as batteries. The invention further provides methods offuel combustion and steam reforming.

In one aspect of the present invention there is a microcombustorcomprising: a first section comprising a combustion fuel channel havingan inlet for connecting the microcombustor to a combustion fuel sourceand an outlet at a top surface of said first section; and a secondsection disposed next to the first section; the second sectionincluding: a combustion chamber having an inlet in fluid communicationwith the outlet of the channel of the first section and an outletcapable of evacuating combustion exhaust products; and an exhaustchannel having an inlet in fluid communication with the outlet of thecombustion chamber and an outlet at a surface of said second section;wherein the combustion fuel channel and the exhaust channel are disposedon a same side with respect to the combustion chamber, so as to form afirst heat exchanger.

In a second aspect, the invention provides a microcombustor thatincludes: a gas inlet connected to a reaction chamber; a liquid feedsystem connected to the inlet of the reaction chamber; a reactionchamber having an internal volume of 100 mm³ or less; an outletconnected to the reaction chamber; and a wick, packed tube or capillarytube disposed in at least one of the inlet or the outlet.

In another aspect, the invention provides a steam reformer, comprising amicrocombustor as described above; and a third section comprising areformation channel having an inlet for supplying reformation fuel andan outlet for evacuating reformation products, wherein the exhaustchannel and at least a portion of the reformation channel are disposedon a same side with respect to the combustion chamber, so as to form asecond heat exchanger.

In another aspect, the invention provides a steam reformer, including: acombustion chamber having an inlet and an outlet, a combustion catalystbeing disposed in the combustion chamber; and a reformation chamberhaving an inlet and an outlet, a reformation catalyst being disposed inthe reformation chamber, wherein the combustion catalyst and thereformation catalyst are disposed on opposite faces of a separationplate disposed between the combustion chamber and the reformationchamber.

In a further aspect, the invention provides a steam reformer, thatincludes: a combustion chamber having an inlet and an outlet, acombustion catalyst being disposed in the combustion chamber; and areformation chamber having an inlet and an outlet, a reformationcatalyst being disposed in the reformation chamber, the combustionchamber and the reformation chamber being disposed around an axis, theinlet and outlet of the combustion chamber being in fluid communicationwith combustion fuel and combustion exhaust channels, respectively, andthe inlet and outlet of the reformation chamber being in fluidcommunication with reformation fuel and reformation products channels,respectively. The combustion fuel channel is disposed along the axis ona side of the combustion chamber opposite the reformation chamber. Thereformation fuel channel is disposed along the axis on a side of thereformation chamber opposite the combustion chamber. The reformationproducts channel is disposed outside the reformation fuel channel withrespect to the axis and on the side of the reformation chamber oppositethe combustion chamber, and the combustion exhaust channel is disposedoutside the reformation fuel channel with respect to the axis and on theside of the reformation chamber opposite the combustion chamber.

In yet another aspect, the invention provides a steam reformer thatincludes: a combustion chamber having an inlet and an outlet; and areforming chamber having an inlet and an outlet. The outlet of thecombustion chamber surrounds the outlet of the reforming chamber, andthe outlet of the reforming chamber surrounds the inlet of the reformingchamber.

In a still further aspect, the invention provides a steam reformer,comprising: a combustion channel comprising a combustion chamber havingan inlet and an outlet; and a reforming channel comprising a reformingchamber having an inlet and an outlet. The reforming chamber has two endsides and a peripheral lateral side. The combustion channel surroundsthe reforming chamber over at least one of the end sides and theperipheral lateral side.

In another aspect, the invention also provides a steam reformercomprising: a first inlet connected to a first reaction chamber; asecond inlet connected to a second reaction chamber; a heat transferplate having first and second major surfaces, the first major surfacebeing in thermal contact with the first reaction chamber, and the secondmajor surface being in thermal contact with the second reaction chamber.The first reaction chamber comprises a combustion catalyst or a steamreforming catalyst, wherein, if the first reaction chamber comprises acombustion catalyst, the second reaction chamber comprises a steamreforming catalyst; or if the first reaction chamber comprises a steamreforming catalyst, the second reaction chamber comprises a combustioncatalyst, and, the first inlet is connected to the first reactionchamber such that, during operation, fluid flows in more than onedirection through the first reaction chamber.

In yet another aspect, the invention provides a steam reformerincluding: a first reaction chamber connected to a first inlet and afirst outlet; and a second reaction chamber connected to a second inletand a second outlet. The first reaction chamber and the second reactionchamber are in thermal communication. The first reaction chambercomprises a combustion catalyst or a steam reforming catalyst, wherein,if the first reaction chamber comprises a combustion catalyst, thesecond reaction chamber comprises a steam reforming catalyst; or if thefirst reaction chamber comprises a steam reforming catalyst, the secondreaction chamber comprises a combustion catalyst. The first inlet andthe first outlet are connected to the first reaction chamber such that,during operation, fluid flows in more than one direction through thefirst reaction chamber between the first inlet and the first outlet.

In a still further aspect, the invention provides a microcombustionprocess that includes: providing a composition comprising combustionfuel and oxidant to a combustion chamber, and passing the compositionthrough a combustion catalyst. The combustion catalyst comprises aporous matrix arranged such that sufficient mixture flows through thecatalyst to maintain combustion at a temperature of at most about 500°C. The composition in the combustion chamber is reacted to producesufficient heat to sustain the microcombustion process without energyinput.

In another aspect, the invention provides a steam reforming process thatincludes: passing a reformation gas through a reforming chamber. Thecombustion of a combustion fuel in a combustion chamber is maintained soas to transfer heat from the combustion chamber to the reformingchamber. The temperature difference between the combustion chamber andthe reforming chamber is at most about 100° C.

In a yet further aspect, the invention provides a method of makinghydrogen gas, comprising: passing a composition comprising H₂O andhydrocarbon into a reforming chamber and reacting the H₂O andhydrocarbon in said reforming chamber to form a hydrogen rich gasmixture. A composition comprising fuel and oxidant is passed into acombustion chamber and, simultaneous to the step of reacting H₂O andhydrocarbon, the fuel and oxidant in the combustion chamber are reactedto produce heat. The reforming chamber and the combustion chamber areseparated by a thermally conductive layer. Heat is transferred from thecombustion chamber to the reforming chamber. The average thermaltransport distance from the combustion chamber to the reforming chamberis 1 mm or less. This “thermal transport distance” is measured from thearea within a combustion zone where combustion occurs. The above aspectof the invention is typically associated with at least one of thefollowing characteristics: (1) at least 80% of the fuel is oxidized inthe combustion chamber and the thermal efficiency of the method is atleast 5%; (2) hydrogen gas production of at least 30 sccm (standardcubic centimeters per minute) H₂ per cc of steam reformer volume; or (3)hydrogen gas production of at least 1 sccm H₂ per cc of device volume.

In yet another aspect, the invention provides a method of steamreforming that includes: passing a reformation gas through a reformingchamber, maintaining combustion of a combustion fuel in a combustionchamber so as to transfer heat from the combustion chamber to thereforming chamber. The reforming chamber is configured such that thevolume of the chamber increases as a function of distance from areaction chamber inlet; and reformation gas and products expand as theypass through the reforming chamber.

In another aspect, the invention provides an integrated combustor,comprising: a combustion chamber comprising a combustion catalyst; anendothermic reaction chamber comprising a catalyst, the endothermicreaction chamber having a length; and a thermally conductive walldisposed between the combustion chamber and the endothermic reactionchamber. The combustion catalyst is disposed on a side of theendothermic reaction chamber such that, during operation, heat from acombustion reaction on the combustion catalyst is transferred along thelength of the reforming chamber, and such that less than 10% of totalheat flux into the endothermic reaction chamber is perpendicular tolength. “Length” is the direction of a chamber that is parallel to flowthrough the chamber. Length, height and width are mutuallyperpendicular. Relatively short deviations in the direction of flow,such as flow from the tube toward and down the separator plate in FIGS.6-7, does not change the direction of length which is determined by theprimary direction of flow through or past a catalyst. This aspectexcludes parallel plate type configurations where a significant (atleast 10%) component of heat transfer is perpendicular to length.

The invention also includes a method of transferring heat to anendothermic reaction in the integrated combustor described in thepreceding paragraph. In this method, a fuel combusts on the combustioncatalyst and generates heat in the combustion chamber. Heat from thecombustion chamber transfers through the thermally conductive wall intothe endothermic reaction chamber and along the length of the endothermicreaction chamber where less than 10% of total heat flux into theendothermic reaction chamber is perpendicular to length. That a fuel“combusts on the combustion catalyst” means contacting a fuel with asolid catalyst, including within a porous catalyst or over a catalystcoating.

In another aspect, the invention provides a method of reforming analcohol in a device having adjacent combustion and steam reformingchambers, comprising: combusting a fuel in a combustion chamber;transferring heat from the combustion chamber across a chamber wall intoa steam reforming chamber; reforming an alcohol at a temperature of 300°C. or less to produce a product stream comprising H₂ in a H₂:CO ratio of70:1 or less. This method has a thermal efficiency of at least 10%.

The invention also provides an integrated combustor/reformer,comprising: a combustion chamber comprising a combustion catalyst; areforming chamber comprising a reforming catalyst; and a thermallyconductive wall separating the combustion chamber and the reformingchamber. The integrated combustor/reformer possesses a thermalefficiency such that when H₂O in a 1.2:1 molar ratio are feed into thereforming chamber at a contact time of 1.0 seconds, and fuel and oxygenare combusted in the combustion chamber at a rate sufficient to obtainan average temperature of 320° C. within the combustion chamber, thereis, at steady-state, a thermal efficiency of at least 10%, and theproduct gas contains 0.5% or less CO.

In another aspect, the invention provides an integratedcombustor/reformer, comprising: a combustion chamber comprising acombustion catalyst; a reforming channel comprising an inlet, areforming chamber containing a reforming catalyst, and an outlet; athermally conductive wall separating the combustion chamber and thereforming chamber. The reforming channel further comprises a methanationcatalyst (1) in direct contact with reforming catalyst, or (2) disposedbetween the catalyst and the outlet wherein there is no H₂-selectivemembrane disposed between the reforming catalyst and the methanationcatalyst and wherein there is not a separate heat exchanger in thermalcontact with the methanation catalyst. The reforming channel has atleast one dimension of 5 mm or less.

The invention also provides a method of reforming an alcohol,comprising: passing a reactant mixture comprising alcohol and water intoa reforming channel comprising an inlet, a reforming chamber, areforming catalyst, a methanation catalyst, and an outlet; passing afuel and an oxidant into a combustion chamber comprising a combustioncatalyst; wherein the fuel in the combustion chamber combusts to produceheat that transfers across a thermally conductive wall into thereforming chamber; maintaining the temperature of the reforming catalystin the range of 200 to 400° C. and maintaining the temperature of themethanation catalyst in the range of 220 to 270° C. There is a portionof reforming catalyst that is closest to a portion of methanationcatalyst and the temperature difference between the portion of reformingcatalyst that is closest to a portion of methanation catalyst and theportion of methanation catalyst closest to the reforming catalyst is 20°C. or less. The reforming catalyst and methanation catalyst are disposedin the reforming channel such that reformed products do not pass througha H₂-selective membrane before contacting the methanation catalyst. Atleast 80% of the alcohol is converted to products and, after contactingthe methanation catalyst, a product stream is produced that contains H₂in a H₂:CO ratio of at least 100 and contains less than 20 mol % of thealcohol present in the reactant mixture.

In another aspect, the invention provides a method of reforming analcohol, in a device having adjacent combustion and steam reformingchambers, comprising: combusting a fuel in a combustion chamber;transferring heat from the combustion chamber across a chamber wall intoa steam reforming chamber and reforming an alcohol to produce a productstream comprising at least 5 sccm H₂ per cc of total device volume in aH₂:CO ratio of 70:1 or less. The device has a total volume of 20 ml orless; and the H₂:CO ratio of 70:1 or less is obtained without aH₂-selective membrane. In a related aspect, the invention provides anintegrated combustor/reformer comprising: a combustion chambercomprising a combustion catalyst; a reforming chamber comprising areforming catalyst; and a thermally conductive wall separating thecombustion chamber and the reforming chamber. The integratedcombustor/reformer possesses a hydrogen productivity such that when H₂Oin a 1.2:1 molar ratio are feed into the reforming chamber at a contacttime of 1.0 seconds, and fuel and oxygen are combusted in the combustionchamber at a rate sufficient to obtain an average temperature of 320° C.within the combustion chamber, there is produced a product streamcomprising at least 5 sccm H₂ per cc of total device volume in a H₂:COratio of 70:1 or less. The device has a total volume of 20 ml or less;and does not contain a H₂-selective membrane. In preferred embodiments,the test conditions use hydrogen and air in the combustion chamber at aH₂:O₂ ratio of 0.5.

The various inventive aspects can be described in combination with anyof the details described in the drawings and the following Descriptionsof the Preferred Embodiments section. For example, the inventive methodscan be further described by combining with the flow rates described inthe Descriptions section. The invention also includes H₂-producingsystems or fuel cell systems that contain any of the combustors and/orreformers described herein. The invention also includes devices underoperating conditions. The invention also includes methods of makinghydrogen, or methods of combustion or steam reforming that utilizes anyof the combustors and/or reformers described herein. In any of theforegoing aspects, there may be a methanation catalyst that is mixedwith a reforming catalyst in the reforming chamber and/or a methanationcatalyst disposed between the reforming chamber and an outlet.

Various embodiments of the invention can provide numerous advantagesincluding one or more of the following. First, light-weight and compactenergy sources can be obtained. Further, the rapid heat and masstransfer in a small device can enable the use of extremely activecatalysts, catalyst which are active at low temperature, and catalystswith high throughput per volume. It is also possible to control processconditions, such as operating temperature, very precisely, so that highperformance can be attained. The fuel combustion and steam reformingprocesses can be stably and efficiently operated at lower temperatures,without the need for energy input to sustain or even to start themicrocombustion process. In some instances, the microcombustor isstarted with hydrogen or vapors such as methanol. Heat losses can beeffectively controlled and reduced. Another advantage is that thesimplicity of the design and the materials used enable mass productionat competitive costs.

Another advantage that results from small size is better control ofheating and uniformity of temperature in a reaction zone. Anotheradvantage is an extremely fast response time, that is, a change in fluidflow can result in a nearly instantaneous change in temperature.

Further, the microcombustor or microreformer can be part of an efficientintegrated system, which can reform lower hydrocarbons and even higherhydrocarbons that require higher processing temperature, such as butane.Carbon dioxide selectivity over carbon monoxide, a poison to fuel cells,of the steam reforming process is high, so that it is possible to avoidor reduce requirements for removing carbon monoxide after reforming andbefore supplying the gas to the fuel cell, thereby greatly simplifyingthe overall system and reducing system size. Since catalytic combustionis used, stable low temperature performance is easily attained for thecombustor to provide uninterrupted operational heat for vaporizers andsteam reformer units so they may operate in a steady optimal manner.

The low temperature operation and manufacturing made possible by theinvention allows a greater choice of insulating materials, enablesgreater use of materials with dissimilar thermal expansion coefficients,and enables manufacture on semiconductor chips. The inventive combustorsand reformers can be made from plastic. There are numerous advantages ofmanufacturing in plastic including low weight and less requiredinsulation.

Additional advantages include: more design options, cheap high volumemanufacturing, eliminating the need for expensive manufacturing machines(compared to the equipment used in silicon processing), and inexpensivematerials.

The subject matter of the present invention is particularly pointed outand distinctly claimed in the concluding portion of this specification.However, both the organization and method of operation, together withfurther advantages and objects thereof, may be better understood byreference to the following description taken in connection withaccompanying drawings wherein like reference characters refer to likeelements.

GLOSSARY OF TERMS

“Catalyst” is a solid material that enhances reaction rate.

“Chamber” refers to the area in which a reaction takes place. In thepresent invention, in embodiments where a catalyst is in the chamber,the area of a chamber includes the catalyst (including pores), the areaabove, below and to the sides of the catalyst, but not the area to theexhaust side of the catalyst. Illustrative examples are shown in thefigures. For example, in FIG. 4 area 426 is part of the reaction chamberwhile 428 is not.

“Channels” refers to the generally accepted meaning and includesconduits and other means for directing the flow of a fluid. Channels ofthe invention include at least one opening, typically with an inlet andoutlet, and may include other openings. As will be seen in thedescription below of various embodiments, numerous functions other thansimple mass transport can occur within channels.

“Fluid communication” between two areas means that a fluid can flow fromone area to the other. “Thermal communication” between two areas meansthat heat can flow from one area to the other.

That “fluid flows in more than one direction” means that there is morethan one fluid flow path. For example, in a straight or curved pipethere is only one fluid flow path (fluid flows in only one direction);while in a pipe with a T-joint, there are two flow paths (fluid flows intwo directions). An example of fluid flowing in more than one directionis shown in combustion chamber 402 of FIG. 4.

“Heat exchanger” is a device or component designed such that heat can betransferred from one fluid to another.

“Layer” refers to a defined area comprising certain listed elements.Typically layers are stacked in multiple-layer configurations.Preferably, layers are planar or substantially planar meaning thatprojections from a layer make up less than 20% of the area of the layer.

A “section” is a layer or portion of a layer.

“Micro,” such as in microcombustor, refers to devices in which there isat least one dimension of a channel or chamber that is 1 mm or less.

“Peripheral lateral side” means a portion of a volume which surrounds acentral portion of the volume and is lateral with respect to a main axisor line of the volume.

“Separator plate” is a solid structural component (e.g., a wall) thatseparates one channel from another channel.

“Thermally conductive” means that a material transfers heat at a ratethat is practical for operation of a device. Examples of thermallyconductive materials include materials such as steel and alumina, whilenon-thermally conductive materials include materials such as Styrofoamand polyurethane. In practice, high thermal conductivity may be balancedagainst factors such as cost, stability, and compatibility.

A “thermal cycle” is heating a device up to operational temperature,operating the device at an operating temperature and observing theresults, and cooling the device to about room temperature.

“Thermal efficiency” is calculated by dividing the lower heating valueof the hydrogen in the reformate stream by the total heating value ofthe methanol fed the reformer plus the heating value of the fuel fed tothe combustor as follows: Efficiency=ΔH_(c)hydrogen/(ΔH_(c)methanolreformer feed+ΔH_(c) combustor fuel feed) where ΔH_(c) is the lower heatof combustion of hydrogen, methanol, or fuel as indicated. This is theequation used to calculate efficiency. ΔH_(c) of the feed will varydepending on the type of feed and conditions and the values can be foundin standard tables such as Perry's Chemical Engineers Handbook.

“Volume” of a combustor, combustion chamber, reformer chamber orreformer, unless otherwise indicated, refers to the internal volumewhere reaction substantially occurs but not adjacent material. Forexample, in FIG. 1 the volume of the combustion chamber is the volume ofcavity 118 (including catalyst 124), in FIG. 3 the volume of thecombustion chamber is the volume of catalyst 316, and in FIG. 4 thevolume of the catalyst 416. Where a catalyst is present, the volumeincludes at least the catalyst volume and catalyst void fraction. Volumeof a device, unless otherwise indicated, refers to the combustor andreformer volume and the volume of any intervening and integralcomponents such as heat exchangers, preheaters, vaporization chambers,recuperators, etc. In FIGS. 1-4 the volume of the device is the volumeof the main body of the rectangular block or largest cylinders, but notthe inlet and outlet tubes that stick out of the main body.

“Wick” is a material that transports liquid, usually the driving forcesfor transport through the wick are capillary forces or a pressuregradient, but other mechanisms such as a graded material with differingdegrees of hydrophilicity could be employed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional side view of a microreformer in a firstembodiment according to the present invention.

FIG. 2 is a cross-sectional front view of the microreformer of FIG. 1along line A-A of FIG. 1.

FIG. 3 is a cross-sectional front view of a microreformer in a secondembodiment according to the present invention.

FIG. 4 is a cross-sectional front view of a microreformer in a thirdembodiment according to the present invention.

FIG. 5 is a schematic view of a steam reforming system according to thepresent invention.

FIG. 6 is a cross-sectional front view of a microreformer in a fourthembodiment according to the present invention.

FIG. 7 is a cross-sectional front view of a microreformer in a fifthembodiment according to the present invention.

FIG. 8 is a data plot of the conversion of CO and consumption ofhydrogen over 3% Ru/alumina (catalyst 0.15 g, 115 cc/min of 75% H₂, 24%CO₂, 0.9% CO plus 3.8 cc/hr H₂O.

FIG. 9 is a data plot of CO methanation as a function of time over 0.2 gof 3% Ru/alumina catalyst in a packed bed (26 mm height, 4 mm innerdiameter) using a feed of 0.6% CO, 15.6% CO₂, 43.8% H₂, and 40% H₂O.

FIG. 10 is a data plot of methanol conversion versus temperature overPd:ZnO on alumina catalysts.

FIG. 11 is a data plot of hydrogen productivity per kilogram Pd versustemperature over various Pd:ZnO supported catalysts.

FIG. 12 is a data plot of methanol conversion and CO selectivity versusweight percent Pd and Pd:Zn molar ratio. This data was collected frommethanol steam reforming at 260° C. over Pd:ZnO on alumina catalysts.

FIG. 13 is a data plot of methanol conversion and mol % CO in theproduct stream at flow rates corresponding to 130, 250, and 400 mW_(t)in the device of FIG. 7, as described in Example 2.

DESCRIPTION OF PREFERRED EMBODIMENTS

The illustrations in the figures are not intended to limit the scope ofthe invention.

A steam reformer of a first embodiment with a layer design is shown onFIGS. 1 and 2. The illustrated steam reformer comprises threesubstantially rectangular layers, namely, a fuel supply layer 102, acombustion layer 104, and a steam reforming layer 106, disposed oneabove the other. These layers are separated by first and secondseparation plates 108, 110, respectively. The layers and plate aredescribed as disposed one above the other with reference to the figures,but the layers could be disposed in other geometric configurations, forexample, they could be formed as sections disposed next to each other.

The fuel supply layer 102 comprises a fuel supply channel 112, which isformed as a substantially longitudinal groove 114 in an upper surface ofthe fuel supply layer. The groove has an open end on a side face of thesteam reformer, while an opposite end 116 of the groove is closedlaterally. The combustion layer comprises a cavity 118, which operatesas a combustion chamber, and an exhaust channel 120, which is disposedsubstantially longitudinally, and is open on both the upper and thelower surface of the combustion and exhaust layer. The fuel supplychannel and the exhaust channel operate as the combustion chamber inletand outlet, respectively.

The combustion chamber is disposed above the laterally closed end of thefuel supply channel, and the first separation plate 108 has an opening122 under the combustion chamber, so that the fuel supply channel andthe combustion chamber are in fluid communication. In the embodimentshown, the fuel supply channel and the exhaust channel are disposed onthe same lateral side of the combustion chamber, and they are preferablyparallel to each other.

A combustion catalyst 124 is disposed in the combustion chamber. Thecombustion catalyst can fill the whole combustion chamber, or a space126 can be provided between the combustion catalyst 124 and the secondintermediary plate 110 as shown on FIG. 1 to allow for fluid expansionand flow to the exit chamber. Various types of catalysts which can beused as combustion catalysts are disclosed in detail below.

The steam reforming layer 106 comprises a reforming channel 128 which isdisposed substantially longitudinally, and is open on the under face andopposite side faces of the steam reforming layer. Thus, a first portionof the reforming channel constitutes a reforming fuel supply channel130, a second portion of the reforming channel constitutes a reformingchamber 132, and a third portion of the reforming channel constitutes areformation products channel 134. The reforming fuel supply channel andthe reformation products channel operate as the reforming chamber inletand outlet, respectively.

The reforming chamber 132 is disposed substantially above the combustionchamber 118, and the reforming fuel supply channel 130 is disposed on asame lateral side of the combustion chamber as the exhaust channel 120,more precisely, the reforming fuel supply channel and the exhaustchannel are preferably parallel to each other. A reforming catalyst 136is disposed in the reforming chamber. The first and second separationplates are made of a heat conductive material, so that heat from thecombustion exhaust in the combustion exhaust channel can be transferred,on the one hand, to the combustion fuel in the fuel supply channel, andon the other hand, to the reforming fuel in the steam reforming channel.Thus, the combustion fuel supply channel 112 and the exhaust channel 120form a first heat exchanger, and the reforming fuel supply channel 130and the exhaust channel 120 form a second heat exchanger. The first heatexchanger makes it possible to vaporize and/or preheat a combustion fuelmixture prior to its delivery into the combustion chamber, and thesecond heat exchanger makes it possible to vaporize and/or preheat areformation fuel mixture prior to its delivery into the reformingchamber.

The catalyst 124 is surrounded by solid material except for a 7° sideopening and a top opening to expansion chamber 126. Exhaust gases travelout of the 7° side opening into open exhaust channel 120. This openingallows gases to flow out of the combustion chamber.

The combustion fuel supply channel 112 is in fluid communication with asource of combustion fuel such as a hydrocarbon fuel, for examplemethanol, and a source of oxidant, for example oxygen in air. As shownon FIG. 2, a combustion fuel tube 138 and an air tube 140 are insertedinto the combustion fuel supply channel. Similarly, the reforming fuelchannel 130 is in fluid communication with a source of reforming fuel,in that a reforming fuel tube 142 is inserted into the reforming fuelchannel. Evacuation of exhaust liquids, in particular liquid water, isfacilitated in that a capillary tube or wick 144 is inserted into theexhaust channel. Exhaust can be expelled into the environment directlyfrom the outlet of the exhaust channel 120, as shown on FIG. 1. In thealternative, the exhaust channel could be connected to an exhaust tubefor evacuating exhaust at a location further away from themicroreformer, or the exhaust channel could be in fluid communicationwith a collecting container so as not to release exhaust fluids into theenvironment. Means of removing liquids, or preventing the formation ofliquids, in the outlet can provide significant advantages—especially insmall devices where the formation of liquid droplets may cause“slugging” and poor device performance.

In another embodiment, a wick can be used to transport liquid into orout of a steam reformer. In some preferred embodiments, a wick isinserted into the exhaust of either the steam reformer or combustor. toexpedite liquid removal from the channels.

A microreformer of a second embodiment according to the presentinvention with a plunger design is shown on FIG. 3. In this embodiment,a combustion chamber 302 and a reforming chamber 304 are disposedopposite a transverse separation surface 306 along a main longitudinalaxis of the microreformer. The separation surface 306 can be aseparation plate. For example, the chambers are cylindrical, eachchamber being formed by a rear wall and a peripheral wall centered onthe main longitudinal axis, the chambers being closed by the separationplate.

Inlet and outlet, respectively 308, 310 are provided on the combustionchamber 302 from a side opposite the separation plate. Similarly, inletsand outlet, respectively 312, 314 are provided on the reforming chamber304 from a side opposite the separation plate. Preferably, the inlet ofat least one chamber being disposed in a central portion relative to themain longitudinal axis and the outlet being disposed in a peripheralportion relative to the main longitudinal axis. For example, the inletand outlet channels are disposed substantially parallel to the mainlongitudinal axis, and tubes forming the combustion inlet channel andthe reforming inlet channel are disposed along the main longitudinalaxis while two tubes forming the combustion outlet channels andreforming outlet channels, respectively, are disposed in symmetricalpositions relative to the respective inlet channel, as shown on FIG. 3.

A combustion catalyst 316 and a reforming catalyst 318 can be placed onopposite faces of the separation plate, for example, as coatings. Fuelscan be supplied into the respective catalysts in that the inlet tubesopen directly against or into the catalyst material. Heat is transferredfrom the combustion chamber to the reforming chamber through theseparation plate.

The catalysts can fill the whole chambers, or a space can be provided ina portion of the respective chamber. For example, a space respectively320, 322 in fluid communication with the outlet channels can be providedin a portion of one or both chambers opposite the separation plate so asto surround the inlet tube, as shown in FIG. 3. In that case, atransverse catalyst plate is preferably disposed in the respectivechamber to separate the portion of the chamber which is filled withcatalyst and the portion of the chamber without catalyst. An advantageof this variant is that outlet gases fill this portion of the chamber orchambers, so that heat can be transferred from the outlet fluids to theinlet fluids.

In the combustion chamber as well as in the reforming chamber, the fuelflows in more than one direction from the inlet to the outlet. In otherwords, the inlet and outlet are disposed such that more than one linecan be traced from the center of an inlet to the center of an outletacross the chamber. In a preferred embodiment, fuel expands radiallythrough a catalyst. In preferred embodiments, gas moves fast near theinlet and then slows as it moves through the catalyst. In some preferredembodiments, the gas is hottest at the center of the catalyst and nearthe inlet, thus providing precise delivery of thermal energy.

In another variant (not shown) of this embodiment, the two outlet tubesof at least one of the chambers are replaced by a single outlet tubesurrounding the inlet tube.

A microreformer of a third embodiment according to the present inventionwith a second plunger design is shown on FIG. 4. In this thirdembodiment, a combustion chamber 402 and a reforming chamber 404 aredisposed on opposite sides of a transverse separation surface 406, forexample a separation plate, along a main longitudinal axis of themicroreformer. A centrally positioned inlet tube 408 parallel to themain longitudinal axis opens into the combustion chamber 402 through itsrear face, i.e., the side opposed to the separation plate, as in thesecond embodiment. However, this embodiment differs from the secondembodiment in particular in that an outlet channel 410 of the combustionchamber is on the side of the reforming chamber 404. More precisely, aninlet channel 412 of the reforming chamber is surrounded by an outletchannel 414 of the reforming chamber, which is formed as an annularchannel. Further, the outlet channel 410 of the combustion chamber isalso formed as an annular channel surrounding both the reforming chamber404 and the outlet and inlet channels respectively 414, 412 of thereforming chamber. This construction makes it possible to transfer heatfrom the reforming outlet to the reforming inlet, also from thecombustion outlet to the reforming chamber and both the reforming inletand outlet.

Catalysts respectively 416, 418 are placed in the respective chambers,for example on or against the separation plate. Advantageously, theinlet in at least one chamber opens directly onto the catalyst.

In this third embodiment, the catalyst can fill the whole or only aportion of each chamber, as in the second embodiment. In the variantshown on FIG. 4, the catalyst fills the whole chamber, a rear exhaustchamber 420 in fluid communication with the combustion chamber and theexhaust channel is provided around the combustion inlet tube, so as totransfer heat from the combustion exhaust to the combustion fuel. Atransverse catalyst plate 422 is disposed between the combustion chamber402 and the rear exhaust chamber, and a transverse catalyst plate 424 isdisposed between the reforming chamber 404 and its outlet 414. Annulararea 426 is the exhaust channel and 428 is the exhaust flow.

Fluid flow is directed such that the heat generated in the exothermicside of the reactor is used to optimize the transfer of heat to theendothermic side of the reactor via conductive heat transfer, and topreheat the fuel streams to achieve vaporization via convection.

Reactants are fed through an inlet formed as a central feed tube suchthat the vaporized feed contacts the respective catalysts at the centersof the catalyst disks. The fluid flows radially, in all directions, outfrom the center of the catalyst disk as a mixture of diminishingconcentration of unreacted fuel to exhaust products. As the fluidmixture diffuses through the catalyst bed, unreacted fuel contactsunused catalyst reaction sites such that all of the fuel is reactedprior to entering the exhaust chamber.

By directing the flow in this manner a temperature gradient isestablished between the center and the outer edges of the catalyst bedwith the highest temperature at the center of the thermally conductivetransverse separator plate located between the two reactor chambers;thus minimizing heat loss through the reactor walls.

The heated exhaust gases typically enter the exhaust chamber attemperatures ranging from 80° C. to 400° C., but preferably above 100°C. High exhaust gas temperatures may be indicative of unreacted fuelentering the exhaust chamber while low exhaust gas temperatures areindicative of a low fuel feed rate, or an unreactive catalyst bed.

FIG. 6 is similar to the embodiment of FIG. 3 except that additionalreforming catalyst 602, 603 and methanation catalyst 604 are disposeddownstream of steam reforming catalyst felt 606. In the illustratedembodiment, the optional plunger 608 is porous, allowing fluid to flowtherethrough. Heat from the combustion chamber 610 is conducted throughseparation plate 612 into catalyst felt 606 and is then carried byconduction and convection through the reforming catalyst bed 602, 603.The steam reforming catalyst 602 could be a powder catalyst that is heldin place by catalyst felt 603. The reforming chamber is defined byreactor walls 612, 613, 615. Many alternatives are possible, forexample, the plunger 608 can be omitted and the reaction chambercompletely or partly filled by a continuous, porous reforming catalyst,catalyst powder, or catalyst pellets. The reformate stream passesdirectly into adjacent methanation chamber 616. The methanation catalystcan be a single material or a mixture of materials such as a methanationcatalyst powder between methanation catalyst felts 618. A smallreforming chamber, such as having a diameter of 5 mm or less providessuperior results by enhancing uniformity of conditions such as reducinghot and cold spots and reducing channeling through a powdered catalyst.

The device illustrated in FIG. 7 is similar to the device of FIG. 6except that a methanation catalyst 702 is placed in contact with thesteam reforming catalyst 704. In this case, the reforming chamber isdefined at one edge by the methanation catalyst 702. Where the catalystsare powders, there will not be a sharp delineation between reforming andmethanation zones and some methanation catalyst powder will intermixwith the reforming catalyst powder so that some methanation catalyst ispresent within the reforming chamber (the reforming chamber volume beingdefined by the volume where there is a significant amount of reformingcatalyst such that a reforming reaction could take place under normaloperating conditions. Methanol and water can be injected at roomtemperature into inlet tube 710 where they will be vaporized by heatconducted through the tube from the methanation and reforming catalysts.

A microreformer can be integrated into a hydrogen producing system asshown schematically on FIG. 5. A microreformer of the present inventionis shown on FIG. 5 as a combustion fuel vaporizer/preheater 502, acombustor unit 504, a reforming fuel vaporizer/preheater 506, areforming reactor 508, and a heat exchanger 510 which directs heat fromthe combustor unit to the combustion fuel vaporizer/preheater, thereforming fuel vaporizer/preheater and the reforming reactor, as shownby arrows 512 on FIG. 5. Each of the combustion and reforming fuelmixtures is provided through at least a pump and valve systemrespectively 514, 516 and a feed line respectively 518, 520. Exhaust isevacuated from the combustor through the heat exchanger 510 and line522. In a fuel cell system, reforming fluids can be treated in anoptional gas clean-up unit 524 before being directed through line 526toward a fuel cell (not shown) where reformation products (including H₂)are combined with O₂ to generate electricity. The secondary clean-upprocess may include a preferential oxidation reactor or a methanationreactor or both, membrane separation of either hydrogen or carbonmonoxide, a sorption based separation system for either hydrogen orcarbon monoxide, and the like.

In practice, fuel processing systems may be significantly more complex.For example, heat from a combustor can also be used to supply heat forother processes such as steam generation (not shown) that can beutilized for a steam reformer, autothermal reactor and water gas shiftreactor. Various fuel cells are well-known and commercially availableand need not be described here. Instead of a fuel cell, thehydrogen-containing gas could, for example, go to: a storage tank, arefueling station, a hydrocracker, hydrotreater, or to additionalhydrogen purifiers.

Combustor/Reformer Characteristics

Materials and Device Manufacture

Various materials or combinations of materials can be used in themicroreformer of the present invention. For example, a metal or aceramic, such as zirconia, is preferably used for the layers while ametal, such a stainless steel, aluminum, brass or copper, is preferablyused for the intermediary plates. The materials are preferably resistantto steam or oxygen corrosion. As a variant, a plastic material, such aspolyimide, is used for the layers only, or for both the layers and theseparation plates. The fuel supply tubes can be plastic or metallic, forexample, stainless steel. A wick is preferably a material such as fibersor foams that utilize capillary forces to transport liquids, such ascotton or felt; alternative means such as hydroscopic materials (e.g.silica) or materials with hydrophilic surface properties may also beemployed as wicks.

In some preferred embodiments, the external reformer/combustor walls areinsulating materials. In some embodiments, there is no elemental siliconor doped silicon in the device, for example, the reactor walls are notcomposed of silicon. To avoid heat loss and increase thermal efficiency,the reactor walls are preferably as thin as possible.

Various components for these microcombusters and microreformers can bemanufactured using standard techniques for producing small metal,ceramic, and/or plastic parts. For example, the body and plungers for acombined reactor assembly can be stamped from a standard metal pressfitted with the appropriate dies, and the end-cap assemblies can beextruded as completely assembled units. Assembly joins the end-capassemblies to the catalyst filled body and plungers via standard partsjoining processes, which may, for example, employ the use of adhesivebonds or metals soldering techniques. When end caps are utilized, theymay be welded, brazed, screwed on, snapped on, or adhered on using ahigh temperature adhesive.

Combustor/Reformer Geometry and Configuration

Reactor configurations include, but are not limited to, the designsdescribed in connection with the figures. The components of anintegrated combustor/reformer may include: a combustion chamber, areforming chamber, a wall separating the combustion and reformingchambers, a preheater or preheat zone, a vaporizer or vaporizing zone,and a methanation chamber or methanation zone. The combustion chamberand reforming chamber are oriented so that heat is transferred from thecombustion chamber into the reforming chamber. Both the combustor andreformer should have a separate preheater (and/or a vaporizer) or apreheat zone (and/or a vaporizer zone) integrated within the device inwhich reactants are preheated (and/or vaporized) prior to contacting acatalyst. For example, preheating/vaporizing can be conducted byconfiguring the devices to have reactant channels adjacent to thecombustion chamber, combustion exhaust channel, reforming chamber,methanation zone, and or reformate product channel.

In some preferred embodiments, heat travels via convection and/orconduction along the length of the reforming chamber. The volume of areforming chamber is defined as the volume containing a packed bedcatalyst or catalyst monolith or the volume containing a catalyst and abulk flow path over the catalyst (such as a wall coating). The length ofreforming chamber is the direction of net flow through the reformingchamber volume. Height and width are mutually perpendicular andperpendicular to length. Preferably, the distance of length of thereforming chamber is at least twice, more preferably at least 4 times,the distance of height or width; this enables excellent alcoholconversion at lower temperatures, thus improving thermal efficiency. Insome preferred embodiments, a reforming channel contains a reformingcatalyst and a methanation catalyst. Configurations in which a reformingcatalyst contacts a methanation catalyst can be particularlyadvantageous because heat can be conducted between the catalysts thatoperate at similar temperatures.

In addition to, or in place of, the preheat chambers, heat exchangerscan be employed to control temperatures of fluids and components in thedevices. The direction of flow in the heat exchangers may be eitherco-current, counter-current, or cross-flow. For some embodiments, thisapproach can enable excellent heat transfer performance.

The combustion chamber preferably has a volume of 0.05 ml or less; morepreferably 0.003 ml or less. In some preferred embodiments, the volumeof the combustion chamber is in the range of 0.02 and 0.002 ml. In someembodiments, a reforming chamber in thermal contact with the combustionchamber has dimensions that are similar to, or the same as, thedimensions of the combustion chamber. In some other embodiments, thereforming chamber has a volume of 10 ml or less; more preferably 1 ml orless; in some embodiments 0.05 ml or less. In some preferredembodiments, the volume of the combustion chamber is in the range of 1and 0.01 ml. In some configurations it is desirable for the reformingchamber to have at least 3 times the volume, more preferably at least 10times the volume of the combustion chamber. The volume of the combustionchamber is the area where catalyst is present, either as a packed bed, aporous monolith, or a wall coating of a channel through which travelsfuel and combustion products.

The overall volume of an integrated microreformer device (includingpreheat, combustion and reforming chambers, and optional methanationzone) is preferably 20 ml or less, more preferably 1 ml or less, and insome embodiments 0.05 ml or less. In some preferred embodiments, thevolume of the integrated microreformer is in the range of 0.01 and 0.2ml.

Heat loss is a function of surface area - lowering surface area (for thesame amount of heat) reduces heat loss and puts thermal energy exactlywhere it is needed. Therefore, in some preferred designs, surface areais minimized. For example, in some environments, cylindrical reformingand/or combustion channels can perform better than planar geometries.

In cylindrical configurations (such as shown in FIGS. 3, 4, 6 and 7),the combustion and reforming chambers preferably have a diameter of 35mm or less, more preferably 15 mm or less; and in some preferredembodiments, the diameter is in the range of 0.74 to 5.0 mm. In layeredconfigurations (such as shown in FIGS. 1 and 2), the combustion layerpreferably has a height (in the embodiment shown in FIGS. 1 and 2,height is the distance between the reformer layer and the combustor fuellayer including one half of the thickness of the two separator plates)of 1 mm or less, more preferably 0.6 mm or less; and in some preferredembodiments, the thickness is in the range of 0.4 to 0.1 mm.

The invention also enables the economical manufacture of arrays ofmicrocomponent devices incorporating hundreds or thousands or more ofmicrocombustors (optionally interleaved or nested with alternatingcomponents such as microreformers or heat exchangers). Devices havingthe described performance characteristics can be relatively largedevices with numerous repeating units; however, in some preferredembodiments, the characteristics (see the following section) areobtained in single, nonrepeating units that are not part of largerrepeating unit devices such as plate reformers.

A complete compact power system can be constructed with liquid and gasdelivery systems, valves, microbattery for start-up, packaging andintegration with a fuel cell. For example, passive liquid deliverysystems (0.03 ml/hr-0.5 ml/hr), gas delivery systems (5 sccm-50 sccm)valves, and appropriate controls can be provided. The system can also beoperated passively, from a start-up time or after an initial expenditureof energy to begin the process.

In preferred embodiments, the integrated combustor/reformer does notcontain any H₂-selective membranes to filter a gas (for example, no Pdmembranes), and/or does not contain any preferential oxidation catalystor oxygen inlets so that no reformate product stream is preferentiallyoxidized.

Combustor/Reformer: System Properties

A significant advantage of the present invention is the ability toprovide microcombustors and microreformers, possessing desirableperformance capability, in sizes that have been heretofore unobtainable.Surprisingly, in methods and devices of the present invention, thesesmall sizes can be accompanied by self-sustaining or better performance.The various combinations of size, flow rates, performance, and othervariables discussed herein are preferred characteristics that can beused to describe the present invention. The characteristics described inthe Operating Conditions section and the following levels of conversionsand/or selectivities and/or thermal gradients and/or thermalefficiencies and/or stabilities are characteristics of some preferredinventive methods. These levels are also characteristic of apparatuswhen it is tested under the following conditions: when H₂O and methanolin a 1.2:1 molar ratio are feed into the reforming chamber with acontact time of 1.0 second, and fuel and oxygen are combusted in thecombustion chamber at a rate sufficient to obtain an average temperatureof 320° C. within the combustion chamber. Preferably, in this test,hydrogen and air are combusted with a feed ratio comprising a H₂:O₂ratio of 0.5.

Alcohol conversion in the reforming channel is preferably at least 50%,more preferably at least 80% and still more preferably at least 90%, andyet more preferably at least 98%. Hydrogen selectivity, defined as molesH atoms in H₂ in the product gas divided by moles H in all productgases, is preferably at least 50%, more preferably at least 60%, stillmore preferably at least 85%. H₂:CO ratio in the product stream ispreferably at least 70, more preferably at least 100; and still morepreferably at least 10,000, and in some embodiments in the range of 100to 100,000.

In the combustion chamber, fuel conversion (as measured by gaschromatography of the exhaust gas) is preferably at least 70%, morepreferably at least 80%, and still more preferably at least 90% andstill more preferably at least 98%. Carbon dioxide selectivity, definedas moles CO₂ in the exhaust gas divided by of allcarbon-and-oxygen-containing product gases, is preferably at least 50%,more preferably at least 70%, still more preferably at least 85%.Conversions higher than 99% and close to 100% for fuels to both thecombustor and for the reformer has been attained.

In some embodiments, the reforming chamber is hottest at one end, andgets cooler along its length. In some preferred embodiments, thetemperature at one end of the length of a reforming chamber is within20° C. of the temperature of the combustion chamber, and that hot end isat least 10° C. higher than the average temperature of the reformingcatalyst.

Thermal efficiency is preferably at least 5%, more preferably at least10% and still more preferably at least about 20%, and in someembodiments 10 to about 35%, in some embodiments 15 to 25%.

The systems preferably are stable such that conversion and/or thermalefficiency decreases by 5% or less after 100 hours of continuousoperation, and, preferably, degrades by 5% or less after 5 thermalcycles. Whether a system “degrades” can be defined (and measured) usingany of the properties and characteristics discussed herein, for example,alcohol conversion, H₂ production, and/or CO levels.

Catalysts

The combustion catalyst can be any known combustion catalyst. Typicalfor the devices described in the examples was 5% Pt on alumina washcoated onto a FeCrAlY felt.

Catalyst compositions suitable for methanol steam reforming includeCuZnAl, Pd/ZnO, and supported Ru, Pt, and Rh catalysts. Pd/ZnO catalystsare preferred since they are not pyrophoric and can possess excellentperformance properties. In preferred embodiments, the steam reformingcatalyst is characterizable as having a H₂ productivity of at least 100Nm3/kg·Pd/h at 240° C. and/or a methanol conversion of at least 70% anda CO selectivity of 2% or less at 260° C. These performance propertiesare to be measured as described in the quartz tube testing procedures ofthe Examples section. In preferred embodiments, Pd/ZnO is dispersed on asupport, preferably a metal oxide support. Alumina is a particularlydesirable support because of its low cost, high surface area, and goodinteraction with Pd/ZnO. In some preferred embodiments, the catalystcontains 2 to 10 weight % Pd (including the weight of the support,typically a metal oxide, upon which the Pd/ZnO is dispersed, but notincluding any underlying material such as a metal felt or foam), and insome embodiments 5 to 10 wt%. In some preferred embodiments, the steamreforming catalyst has a Pd:Zn molar ratio of 0.1 to 0.8, morepreferably 0.2 to 0.5, and still more preferably 0.30 to 0.45. In somepreferred embodiments, a Pd/Zn catalyst is prepared by co-precipitatingPd and Zn; these components may be coprecipitated using inorganic ororganometallic precursors. Prior to steam reforming, the steam reformingcatalyst is advantageously subjected to an activation treatment,preferably reduction at 300-400° C.

In some embodiments, methanation catalysts for use in the presentinvention can be any of the known methanation catalysts. In preferredembodiments, the methanation catalyst has ruthenium distributed on thesurface of an alumina support, in some preferred embodiments Ru ispresent in a range of 2 to 4%. In some preferred embodiments, the weightratio of Ru to alumina is at least 0.03, and in some embodiments, 0.03to 0.1. In some particularly preferred embodiments, a Ru/Al₂O₃ catalystis disposed over the surface of a porous support such as a felt.

The function of the methanation catalyst is to reduce CO in the outputof the reformer. Therefore, the methanation catalyst should be disposedso that CO produced in the reforming reaction can be converted tomethane. Because methanation catalysts can operate at temperatures thatare similar to or the same as reforming catalysts, the methanationcatalyst can be disposed in contact with the reforming catalyst, eitheradjacent or mixed with a reforming catalyst. If it is mixed, this mixingshould preferably be in the downstream portion of the reforming catalystso that methanation of methanol doesn't occur.

Particularly useful for any of the combustion, reforming and/ormethanation catalysts are catalysts having very high porosity, forexample, at least about 80%, and large pore sizes, for example, up to200 μm, so as to facilitate a high mass transfer at low pressuredifferential. Such catalyst is a preferred way to maintain a small-sizereactor. A very high activity catalyst is not required, but highactivity catalysts can be used, which can result in smaller devices withlarger processing rates.

The catalysts may take any conventional form such as a powder or pellet.In some preferred configurations, a catalyst includes an underlyinglarge pore support. Examples of preferred large pore supports includecommercially available metal foams and, more preferably, metal felts.The large pore support has a porosity of at least 5%, more preferably 30to 99%, and still more preferably 70 to 98%. Preferably, the support hasa volumetric average pore size, as measured by BET, of 0.1 μm orgreater, more preferably between 1 and 500 μm. Preferred forms of poroussupports are foams and felts and these are preferably made of athermally stable and conductive material, preferably a metal such asstainless steel or FeCrAlY alloy. These porous supports can be thin,such as between 0.1 and 1 mm. Foams are continuous structures withcontinuous walls defining pores throughout the structure. Felts arefibers with interstitial spaces between fibers and includes tangledstrands like steel wool. Various supports and support configurations aredescribed in U.S. patent application Ser. No. 09/640,903 (filed Aug. 16,2000), which is incorporated by reference.

A catalyst with a large pore support preferably has a pore volume of 5to 98%, more preferably 30 to 95% of the total porous material's volume.Preferably, at least 20% (more preferably at least 50%) of thematerial's pore volume is composed of pores in the size (diameter) rangeof 0.1 to 300 microns, more preferably 0.3 to 200 microns, and stillmore preferably 1 to 100 microns. Pore volume and pore size distributionare measured by mercury porisimetry (assuming cylindrical geometry ofthe pores) and nitrogen adsorption. As is known, mercury porisimetry andnitrogen adsorption are complementary techniques with mercuryporisimetry being more accurate for measuring large pore sizes (largerthan 30 nm) and nitrogen adsorption more accurate for small pores (lessthan 50 nm). Pore sizes in the range of about 0.1 to 300 microns enablemolecules to diffuse molecularly through the materials under most gasphase catalysis conditions.

In preferred embodiments, the surface active sites of a catalyst aredispersed on a (preferably high surface area, BET surface area>10m²/g)metal oxide support. Preferred metal oxides include ZnO, ZrO₂, andAl₂O₃. The metal oxide, including the presence of catalytically activesurface sites, as measured by BET, preferably has a volumetric averagepore size of less than 0.1 micrometer (μm). The metal oxide, includingthe presence of catalytically active surface sites, as measured by BET,nitrogen physisorption, preferably has a surface area of more than 10m²/g, more preferably a surface area of 20 to 500 m²/g. The metal oxidecan be particles, preferably having diameters less than 100 μm, morepreferably less than 10 μm, or, more preferably, forms a layer (ofagglomerated particles or a continuous film) having a thickness lessthan 100 μm, more preferably less than 50 μm, and still more preferablya thickness of less than 10 μm.

When an underlying, large-pore substrate is used, a powder can be slurrycoated over the substrate at any stage in the preparative process. Forexample, a high surface area metal oxide could be slurry coated onto thesubstrate followed by depositing, drying and activating a metal via theimpregnation method. Alternatively, a vapor coat or soluble form ofalumina (or other high surface area material) could be applied onto thesubstrate. Although solution or slurry coating is typically lessexpensive, vapor coating of the various materials could also beemployed.

Porous catalysts can be prepared, for example, by wash-coating on aFeCrAlY felt (obtained from Technetics, Deland, Fla.) where the felt issized to have a 0.01″ (0.25 mm) thickness and 90% porosity. In someembodiments, the mass of wash coat may be in the order of 0.1 gramcatalyst per square inch (6.5 cm²) of felt. Coatings can also be appliedto other types of structured substrates like metal foams made ofstainless steel, copper, alloys, etc. In one preferred embodiment, thelarge-pore substrate has a corrugated shape that could be placed in areaction chamber (preferably a small channel) of a steam reformer.

In the illustrated devices, the catalysts are porous, flow-throughcatalysts in which flow proceeds chiefly through the catalyst structure.In some alternative embodiments, the catalyst can be placed on an innerwall or on inner walls of the reaction chamber with an open channel fromthe reactor inlet to the outlet—this configuration is called “flow-by.”In other alternative embodiments, the catalyst can be packed in the flowpath.

Preferred embodiments of the inventive microreformers and methods mayalso be described in terms of the exceptionally high specific activityof the catalysts. Preferably, the catalyst and/or method has a specificactivity of greater than 1.5, more preferably greater than 2.5 molmethanol converted/(g catalyst)(hr) when tested at 400° C., 25 mseccontact time, 1.8 steam-to-carbon (i.e., water:methanol) ratio; and thecatalyst exhibiting this specific activity preferably has a pressuredrop of less than 25 psig.

Operating Conditions

Operation of a microreformer according to the present invention will nowbe described. An exemplary start-up procedure begins at room temperaturewith slow flow of H₂ gas (0.2-0.5 sccm) and low flow of air 5-8 sccm.After light-off, hydrogen flow is increased until reactor temperatureis >70° C. (usually around 1-1.5 sccm H₂). Fuel flow to combustor can beinitiated at this point. Once the fuel (preferably methanol) has begunreacting (the combustor temperature will increase substantially), thehydrogen flow is tapered off and the fuel flow is increased. A minimumof 10% excess air was maintained to ensure that the combustion catalystwas able to convert 100% of the fuel. The excess air should not be toomuch (preferably below 200%), since the extra air removes heat from thesteam reformer. Air and methanol flows are adjusted until the steamreformer is at the desired temperature or 10-20° C. greater. Thereformer fuel mixture flow is initiated at this point. Combustor flowsare adjusted as necessary to maintain desired temperatures.

Steam reforming is a process in which hydrogen is stripped from ahydrocarbon fuel by thermal energy provided by a combustor. The processcan be represented by the chemical equation:C_(a)H_(b)O_(c)+(2a−x−c)H₂O=x CO+(a−x)CO₂+(2a−x−c+b/2)H₂

In alcohol steam reforming, the feed stream contains steam and analcohol or alcohols. In the present invention, methanol, ethanol, andpropanol are preferred with methanol being especially preferred. Thereformer mixture molar ratios are preferably between 1-6 steam:carbon,and more preferably between 1.5-3 steam:carbon. In a particularlypreferred embodiment, the feed stream into the reforming chambercomprises methanol and water in a ratio of 1:1 to 1:3. The flow rate ofreactants will depend on the desired amount of H₂ to be produced and onthe minimum or maximum capacity of the steam reformer. In some preferredembodiments of the present invention, the steam reformer fuel mixtureflow rates are preferably between 0.005 and 1.0 ml/hr and morepreferably between 0.05 and 0.2 ml/hr, where volume is volume of thealcohol and water at room temperature.

The rate of combustion can be controlled to provide the desired amountof heat to a steam reforming reaction in an adjacent reforming chamber.In some preferred embodiments of the present invention, the fuel(preferably methanol) and air flow rates to the combustor are preferably0.01 to 5 ml/hr, where volume is volume of the fuel at room temperature,and 1-50 sccm, respectively and more preferably 0.1 to 0.5 ml/hr and5-15 sccm respectively.

The steam reforming reaction can be run over a broad pressure range fromsub-ambient to very high. The alcohol steam reforming reaction ispreferably carried out at 200-400° C., more preferably 220-300° C., andin some embodiments 240-270° C. In some preferred configurations, thecombustion temperature is approximately the same (that is, within 20°C.) as the average reformer temperature (that is, the averagetemperature of the reforming catalyst). The pressures are preferablybetween 0 and 10 psig and more preferably between 0 and 2 psig for boththe combustor and the reformer. In some preferred embodiments, contacttime (based on steam reforming catalyst) of the reforming process streamis less than 2 seconds, in some embodiments 1 second or less, and insome embodiments, in the range of 100 ms to 500 ms.

The reformate stream usually comprises hydrogen, carbon dioxide, andcarbon monoxide. PEM fuel cells operate have a very low tolerance forCO. They can generally tolerate carbon dioxide and some other gases suchas nitrogen, but only up to a certain amount. Clean-up of a reformatestream can be performed, for example by a multi-step process consistingof water gas shift reactors, combined with selective oxidation and/orcarbon monoxide methanation, or by the use of a hydrogen permeablemembrane, as disclosed in Pietrogrande et al., “fuel processing,” FuelCell Systems, Chap. 4, Blomen, L J M J and M N Mugerwa, pp. 121-151,Plenum Press, New York, 1993.

We have surprisingly discovered that, in the inventive method, excellentresults can be obtained by directly methanating a reformate streamwithout first passing the reformate through a hydrogen-selectivemembrane, preferential oxidation, or water gas shift reactor. This ishighly desirable since hydrogen-selective membranes are expensive, andadditional process steps can be costly and result in lowered yield.Eliminating the requirement of a preferential oxidation also eliminatesthe need to add oxygen (for example, eliminates the need for added air),including the need to vary oxygen content to account for fluctuations inCO concentration. In preferred embodiments, the process adds heat to thesteam reforming step but does not have additional heat exchangers orheat exchange steps for methanation or for other CO-reducing steps.

The methanation reaction is preferably conducted at below 290° C.,preferably in the range of 220 to 270° C., more preferably 230 to 260°C., where these temperatures refer to the average temperature of amethanation catalyst (in a device) during operation. Temperature of themethanation catalyst is inversely related to contact time. Contact timefor the methanation reaction is preferably less than 2 seconds, morepreferably in the range of 200 to 800 ms. When the methanation catalystis mixed with or adjacent to a reforming catalyst, it is most desirablefor the temperature of the methanation reaction to be similar to thetemperature of the reforming reaction, preferably the averagetemperature of these reactions is 50° C. or less, more preferably 30° C.or less, and still more preferably 20° C. or less.

In another alternative, a reforming channel may contain a reformingzone, a water-gas shift reaction zone (preferably operating at 220 to270° C.), and a methanation zone. In this method also, heat can betransferred along the length of the reforming channel; the reformingzone (the portion of the channel containing reforming catalyst) isnearest the combustion chamber, then the water-gas shift zone, and thenthe methanation zone. Heat generated by the water gas shift reaction canpreheat (and can vaporize) a feed stream.

The following descriptions of the product stream can be measured aftersteam reforming alone, or steam reforming and methanation reactions. Theproduct stream preferably contains at least 20 sccm H₂ per cc of steamreformer volume, more preferably at least 200 sccm H₂ per cc of steamreformer chamber volume, in some preferred embodiments between 20 and5000 sccm H₂ per cc of steam reformer chamber volume, and in someembodiments between 20 and 500 sccm H₂ per cc of steam reformer chambervolume. Alternatively, the product stream preferably contains at least 1sccm H₂ per cc of device volume, more preferably at least 5 sccm H₂ percc of device volume, still more preferably at least 10 sccm H₂ per cc ofdevice volume, and in some preferred embodiments between 6 and about 15sccm H₂ per cc of device volume. In some preferred embodiments, anintegrated combustor/reformer produces 0.5 sccm to 5.0 sccm of H₂. Inpreferred embodiments, more than 80%, more preferably more than 95%, andstill more preferably more than 98% of the alcohol in the fed isconverted to products, and the product stream comprises less than 1.0volume % CO, more preferably 300 ppm or less, still more preferably lessthan 100 ppm, and in some embodiments, about 10 ppm to 90 ppm CO. Theproduct stream preferably has a H₂:CO ratio of at least 70, morepreferably at least 100.

Additional operations can be added to improve performance. For example,unreacted hydrogen from a fuel cell and/or methane from the methanationreaction can be recycled into the combustor.

EXAMPLES Example 1

An integrated fuel processor system composed of twovaporizers/preheaters, a reformer, catalytic combustor, and heatexchanger was built and tested. For each of these designs themanufacture and assembly were performed in the same fashion. Metalpieces were cut and machined from standard stainless steel stock.Ceramic pieces were formed and machined using standard ceramics moldingand shaping techniques. Tubing and fittings were cut to fit as required.

The following example is for a device such as illustrated in FIG. 3. Forpreassembly, all of the tubing, catalyst pieces, and respective reactorparts were cut per specifications. Plungers were joined to tubing usingstandard, high-temperature adhesives. In the alternative,high-temperature soldering could be used for some or all joins. Alltubing and the plunger assemblies were inserted through the end-caps orend-seals and set to their appropriate positions for final assembly.

The first step in the assembly process was to insert the catalyst piecesinto their respective chambers, and then attach the end-caps or sealssuch that the plunger bodies were pressed tightly against theirrespective catalysts. In the second step, the end-caps were thenattached permanently to the reactor body by applying high-temperatureadhesive or by high-temperature soldering.

Catalytic combustion was used to provide heat for liquid vaporization,gas preheating, and to provide the necessary energy for the reformingreaction or reactions. The reformer had a volume of 2.5 mm³ and acapacity of 200 mW_(t). The combustor volume was 2.5 mm³ and had acapacity of up to 3 W_(t). The combustor capacity was oversized in orderto allow a wide range of operating conditions to be examined. Thecombustor fuel consisted of hydrogen and methanol. A thermal couple wasinserted into the combustor to monitor the device temperature. Thesystem was mounted inside a larger tube for testing.

The test stand consisted of syringe pumps, gas controllers, vapor liquidseparations units, and an online gas chromatograph. Syringe pumps fedthe methanol/water mixture to the reformer at rates of 0.02 cc/hr to 0.1cc/hr (20° C. basis), and pure methanol to the combustor at ratesbetween 0.1 cc/hr to 0.4 cc/hr (20° C. basis). Air was fed to thecombustor at rates between 8 and 20 sccm. The product reformate gaseswere fed, via a dri-rite tube to eliminate any residual water vapor, toan on-line micro gas chromatograph (Agilent QuadH).

The use of electric heating for system start-up was eliminated byfollowing the subsequent procedure. Hydrogen and air were fed tocombustor to initiate combustion and heat the vaporizers. Once thevaporizers were heated to approximately 80° C., methanol was fed to thevaporizer. The hydrogen was slowly tapered off as the methanol feed wasincreased until only methanol and air were being fed to the combustorand the device was completely self-sustaining. The methanol/air mixturewas adjusted until the steam reformer reached the desired temperatures(250° C.-450° C.) depending on the conditions being tested. Themethanol/water solution feed was then initiated.

The reformer was operated over a wide range of conditions. In order toachieve 90% conversion, 425° C. operating temperatures in the combustorwere required. Two hundred mW_(t) power was achieved with a thermalefficiency of 10%. A 1/10,000 inch (2.5 μm) diameter thermocouple thatwas used to measure temperature was a major source of heat loss throughthe thermocouple. The efficiency could be substantially improved byremoving the thermocouple and by use of improved insulator materialssuch as metallized polyimide (that reflects heat), and it is believedthat with these improvements the inventive devices can be 25% thermallyefficient.

with a catalyst composed of Pd on ZnO, the reformate stream was composedprimarily of hydrogen (>73%), with approximately 26% carbon dioxide and1% carbon constituting the rest of the components.

The anticipated electrical power from a fuel cell powered by this streamcan be found by multiplying the thermal power by the net fuel cellefficiency. Typical fuel cells operate at 60% efficiency and utilize80-85% of the H₂ in a reformate stream for a net efficiency of about50%. Thus, a fuel cell utilizing the reformate from this device couldprovide on the order of 100 mW_(e), and the system (reformer+fuel cell)would have a net (fuel processor+fuel cell) efficiency of about 4.5%. Asthe reformer output was decreased, the efficiency also decreased. Forexample when the reformer produced 70 mW_(t) (about 35 mW_(e)) theefficiency decreased to 3% (about 1.5% net). The efficiency decreasedbecause the thermal losses as a percent of the total amount of power fedto the device increases as the size is reduced.

The data in the following table was acquired using the experimentalprocedure described above. The gas composition was determined using theAgilent MicroQuad GC, the gas flow rates were determined using a bubblemeter (measure the time it takes for a bubble to move through knownvolume which in this case was 0.2 cc). The gas flow rate was determinedwhen ambient temperature was 19.5° C., thus to standardize it (gas flowat 0° C.), the flow rate was divided by 292.5K (19.5° C.) and multipliedby 273K (0° C.). This results are in sccm or standard cubic centimetersper minute. The methanol conversion was calculated by using a carbonbalance on the system. (e.g., the amount of carbon fed to the reformeris known, and the amount of carbon in the gas can be calculated from theamount of CO, CO₂, and methane formed. Dividing the two numbers givesthe methanol conversion). The data has about a 5% standard deviation.

Cntct Time Approx SR Exit Flow Methanol H₂ flow H₂/SR rctr vol H₂/devicevol Thermal Pwr Effncy mSec Temp, ° C. ccm Conversn sccm scc/(min*cc)scc/(min*cc) mW % 133 398 0.714 1.047 0.45 206 4.49 80.7 6.5 133 3980.698 0.999 0.43 197 4.28 76.9 6.2 86 419 1.092 1.021 0.69 318 6.91124.3 8.4 50 421 1.202 0.628 0.75 346 7.53 135.5 8.5 50 450 1.604 0.8571.02 468 10.17 182.9 9.8 50 450 1.493 0.796 0.94 434 9.44 169.8 9.1 50470 1.644 0.888 1.05 483 10.52 189.1 9.5 50 470 1.671 0.903 1.07 49110.69 192.2 9.7 50 470 1.671 0.901 1.07 491 10.68 192.0 9.7 112 3620.802 0.766 0.33 153 3.33 59.8 5.0 112 363 0.893 0.880 0.39 180 3.9270.5 5.9 112 361 0.875 0.923 0.39 181 3.94 70.9 5.9 133 369 0.677 0.9380.34 158 3.43 61.7 5.5 133 370 0.711 0.958 0.33 150 3.26 58.6 5.2 133370 0.656 0.890 0.28 129 2.81 50.4 4.5 86 371 0.896 0.752 0.40 182 3.9571.1 6.0 86 372 0.951 0.792 0.38 174 3.78 67.9 5.8 86 372 0.929 0.7710.34 156 3.40 61.1 5.2 86 400 0.798 0.698 0.28 129 2.80 50.3 3.9

Example 2

The device illustrated in FIG. 7 was fabricated similarly to thedescriptions in Example 1. The combustion catalyst was Pt on aluminathat was coated onto a FeCrAlY felt support. On the reforming side ofthe device, a porous reforming catalyst felt was inserted into thechannel. The diameter of the felt (0.26 inch, 0.66 cm) was the same asthe inner diameter of the cylinder. Then, a porous plunger (having acenter hole through the center with an inlet tube through the hole) waspressed onto the catalyst felt. In this case, the porous plunger wasalso a porous reforming catalyst felt. Prior to insertion, a laser wasused to form a hole in the center of the porous plunger. Alternativetechniques such as punching a hole through a felt prior to depositing acatalyst coating may alternatively be used. The reforming catalyst feltswere prepared by coating a FeCrAlY felt with alumina followed bydepositing Pd.

Then, 16 mg of a steam reforming powder catalyst was poured in. Thiscatalyst was prepared by coprecipitating Pd and Zn onto alumina powder.Then, 12 mg of a methanation powder catalyst was added onto thereforming powder catalyst. The methanation catalyst was 3 wt % Ru onalumina. A 0.66 cm diameter methanation catalyst felt was placed overthe powder catalysts, and cap was placed to close the tube. The cap wasbrazed in place. The methanation felt was the methanation powder washcoated onto a felt.

The device was operated under conditions similar to those in Example 1.Operational temperatures in the combustion chamber were 315 to 350° C.and combustor flow rates were 6 to 9 cc/min with higher temperaturescorresponding to higher flow rates. A mixture of hydrogen and air werefeed to the combustion chamber at an hydrogen:oxygen ratio of 0.45 to0.6. For testing in which only steam reforming powder catalyst waspresent (no methanation catalyst), combustor temperature ranged from 240to 285° C. at flow rates of 4.8 to 7.1 cc/min. These flow rates are atroom temperature. Start-up procedures were the same as in Example 1except using lower temperatures. Test of the device with contact times(based on steam reforming catalyst) of 1.0 second and 1.5 secondsresulted in product streams containing 0.3 vol % and 0.02 vol % (200ppm).

Methanol and water were fed into the reforming chamber at a 1.2:1 ratio.

Pressure drop through the combustion and reforming sides was very low,in the range of 1-15 psig (pounds per square inch), usually less than 1to 2 psig.

The reactor produced over 13 sccm hydrogen per cm³ of total processorvolume (includes combustion chamber, steam reforming chamber,methanation zones, heat exchangers and vaporizers) or 28 sccm hydrogenper cm³ steam reforming chamber volume (which in this case was thevolume of steam reforming catalyst). The carbon monoxide content in theproduct stream exiting the device was less than 300 ppm and in mostinstances less than 100 ppm. We have shown in simple tube test devicethat CO concentrations of less than 10 ppm can be achieved. A plot ofmethanol conversion and mol % CO in the product stream at flow ratescorresponding to 130, 250, and 400 mW_(t) is shown in FIG. 13. Thethermal efficiency ranged from 8% to over 18% efficient. This efficiencywas lower than when operating without the methanation catalyst (chamberfilled solely with steam reforming catalyst). This was due to higheroperating temperatures and hydrogen loss to methane and waterproduction. The device exhibited excellent stability, running for morethan 65 hours, including 11 thermal cycles, without degradation ofperformance.

In testing in the same type of device without methanation catalyst, thehydrogen production per volume was the same; however, the efficiency wasmuch higher—up to about 33%. However, the CO output was higher—about 1%compared to 300 ppm in the device with the methanation catalyst. Thetypical volume percent CO for the reactor at lower flowrates (e.g. atinlet flow of 0.15cc/hr—was 0.5-0.6%, compared to 0.9-1.0% at a flowrateof 0.2 cc/hr; it is believed that the higher CO was due to the highertemperatures.

Catalyst Testing in Fixed Bed Testing Apparatus

Various methanation catalysts were tested in a fixed bed quartz tubewith a 4 mm inner diameter. This testing showed that Ru on alumina(particularly when the ratio of Ru:alumina was 0.03 or greater)exhibited superior performance compared to other catalysts such as 0.5%Ru on zirconia. The results of passing a stream containing 75% H₂, 24%CO₂, 0.9% CO at a rate of 115 cc/min combined with 3.8 cc/hr of waterthrough a 3% Ru/alumina catalyst are illustrated in FIG. 8. Attemperatures higher than 290° C. the reverse water gas shift reactionwas forming more CO than was being consumed by methanation. However,below 270 C, the catalyst exhibited excellent selectivity toward COmethanation. FIG. 9 shows the results of methanation over the samecatalyst as a function of contact time and temperature. At temperaturesin the range of 240-270° C. and a contact time of 120 ms, less than 50ppm CO was achieved.

Steam Reforming Catalyst Testing

For comparison purposes, a supported Pd—ZnO catalyst was fabricated viathe formation of zinc oxide on a y-alumina support by the precipitationof zinc hydroxide from a zinc nitrate solution with ammonia at pH about8 and calcination at 350° C., followed by Pd incipient wetnessimpregnation. The catalysts prepared by this precipitation route arehereafter referred to the baseline catalyst.

Other supported Pd—ZnO catalysts were prepared by a one-stepco-impregnation method. In this method, a concentrated palladium nitratesolution (containing about 20 wt % Pd in nitrate acid solution) wasmixed with solid Zn(NO3)₂.6H₂O at 50 to 80° C. in order to obtain asolution containing Pd and Zn as concentrated as possible. The ZnO/Pdratio in the resultant solution was varied from 0.7 to 25 in order toobtain the final products having Pd loadings of 1 to 15 wt %. A givensupport was impregnated at 50 to 80° C. with the amount of solutionadjusted according to the pore volume of the support. The wet sample waskept at 60° C. at least one hour that allowed completing theimpregnation process. The samples were dried in air and then calcined at350° C. for 3 hours. A series of Pd—ZnO/Al₂O₃ with varying Pd loadingsusing the one-step co-impregnation method have been fabricated. In orderto investigate the support effects, ZrO₂ and Ce₂O₃ supported Pd—ZnOcatalysts were also be made.

A typical Pd—ZnO/Al2O3 using the one-step co-impregnation method forfabricating is described as follows.

-   -   1. A mixture containing 13.10 g of Zn(NO3)₂.6H₂O and 1.773 g of        concentrated Pd nitrate solution (20.19 wt Pd) was heated at        60° C. in a water bath till the solids dissolved.    -   2. A 2.00 g of g-Al₂O₃ powder with 60-120 mesh (preheated at        500° C. for 2 h) was impregnated with 3.077 g above solution in        a glass vial and kept at 60° C. for at least one hour.    -   3. The wet sample was dried at 100° C. and then calcined at        350° C. at 20° C./min for 2 hours.        The final composition of the catalyst contained 2.6 wt % of Pd,        26 wt % of ZnO, and 70.2 wt % of Al₂O₃. Other catalysts were        fabricated in similar ways and their compositions are listed in        Table 1.

TABLE 1 Composition of supported Pd/ZnO catalysts. Composition, wt %Sample Description Pd ZnO Support (baseline) ZnO:Pd = 8, on Al₂O₃ 8.6 7021 PdZnAl-10 ZnO:Pd = 10, on Al₂O₃ 2.6 26.4 71.0 PdZnAl-4.5 ZnO:Pd =4.5, on Al₂O₃ 5.0 22.8 72.2 PdZnAl-2 ZnO:Pd = 2.0, on Al₂O₃ 8.9 17.873.3 PdZnAl-1 ZnO:Pd = 1.0, on Al₂O₃ 12.9 13.0 74.1 PdZnAl-0.7 ZnO:Pd =0.7, on Al₂O₃ 15.7 10.9 73.4 PdZnZr-10 ZnO:Pd = 10, on ZrO₂ 1.9 19 79.1PdZnCe-10 ZnO:Pd = 10, on Ce₂O₃ 1.4 14 84.6

The steam reforming catalysts were tested in the fixed-bed quartztubular reactor with a 4 mm I.D. In each case, the packed catalysts werereduced at a hydrogen-containing gas at 400° C. for 3 hours prior toreaction. The feed liquid consisted of methanol and water at a weightratio of 1. In most cases, about 0.192 g of the catalyst was used at afeed rate of 2 ml/h.

Table 2 list some results for steam reforming of methanol over selectedcatalysts fabricated according the reported method. The results showthat all the examined catalysts, except for the Ce₂O₃ supportedcatalyst, demonstrate the high activity (80% conversion of methanol atbelow 300° C.) and very low CO selectivity (less 0.8% CO in the dryproduct steam) while retaining fairly high H₂ productivity.

TABLE 2 Reaction results at a 80% of methanol conversion for supportedPd—ZnO. Results at Conversion of 80% T₈₀ Selec. of CO₂ % CO in Dry H₂Productivity Sample [° C.] % Product Stream [Nm³/kg cat · h] (baseline)297 97.7 0.52 8.2 PdZnZr-10 295 97.8 0.80 8.2 PdZnCe-10 305 86.0 3.602.7 PdZnAl-10 275 97.8 0.58 8.9 PdZnAl-4.5 265 98.3 0.42 7.3 PdZnAl-2250 98.6 0.36 8.5With a similar amount of Pd content, the catalyst (PdAlZn-2, 8.9 wt %Pd) which was made by the co-impregnation method exhibits much higheractivity than that of the baseline catalyst (8.6 wt % Pd), which wassynthesized by a precipitation and impregnation process. At the 80%conversion of methanol, the reaction temperature difference is about 50°C. Conversion of methanol over PdAlZn-2, PdZnAl-4.5, PdZnAl-10, and thecomparative baseline, as a function of temperature is shown in FIG. 10.As can be seen in the figure, the coprecipitated catalyst exhibitssignificantly superior activity over a broad range of temperatures.

Furthermore, over the catalysts supported by different substrates, suchas Al₂O₃, ZrO₂, and Ce₂O₃ prepared using the improved method, the H₂productivities of steam reforming of an alcohol (in this case, methanol)are much higher than that of the baseline catalyst. The results areshown in FIG. 11.

FIG. 12 shows the conversion of methanol and selectivity to CO atvarying Pd loadings (wt %) and Pd to Zn ratios at 260° C. Surprisingly,it was observed that alcohol conversion decreased with increasing Pdlevels above about 9% and above a Pd:Zn ratio of about 0.4.

CLOSURE

While preferred embodiments of the present invention have been shown anddescribed, it will be apparent to those skilled in the art that manychanges and modifications may be made without departing from theinvention in its broader aspects. For example, although devices areshown with one combustor and one reformer, numerous variations such astwo combustors sandwiching one reformer, and these variations areincluded within the scope of the invention. The appended claims aretherefore intended to include all such changes and modifications as fallwithin the true spirit and scope of the invention.

1. An integrated combustor, comprising: a combustion chamber comprisinga combustion catalyst; an endothermic reaction chamber comprising acatalyst, the endothermic reaction chamber having a length; a thermallyconductive wall disposed between the combustion chamber and theendothermic reaction chamber; wherein the combustion catalyst isdisposed on a side of the endothermic reaction chamber such that, duringoperation, heat from a combustion reaction on the combustion catalyst istransferred along the length of the endothermic reaction chamber, andless than 10% of total heat flux into the endothermic reaction chamberis perpendicular to length.
 2. The combustor of claim 1 wherein thecatalyst in the endothermic reaction chamber comprises a steam reformingcatalyst.
 3. The combustor of claim 2 wherein the length of theendothermic reaction chamber is at least two times more than the lengthof the combustion chamber.
 4. The combustor of claim 3 wherein catalystsubstantially fills the endothermic reaction chamber.
 5. The combustorof claim 3 wherein the endothermic reaction chamber is part of areforming channel and further wherein a methanation catalyst is disposedin the reforming channel.
 6. The combustor of claim 5 wherein thereaction channel is a microchannel.
 7. An integrated combustor/reformer,comprising: a combustion chamber comprising a combustion catalyst; areforming chamber comprising a reforming catalyst; wherein the reformingcatalyst comprises Pd and is characterizable as having a H₂ productivityof at least 100 Nm³/kgPd/h at 240° C.; a thermally conductive wallseparating the combustion chamber and the reforming chamber; and whereinthe integrated combustor/reformer is characterizable by a thermalefficiency such that when H₂O and methanol in a 1.2:1 molar ratio arefeed into the reforming chamber at a contact time of 1.0 seconds, andfuel and oxygen are combusted in the combustion chamber at a ratesufficient to obtain an average temperature of 320° C. within thereforming chamber, there is, at steady-state, a thermal efficiency of atleast 10%, and the product gas contains 0.5% or less CO.
 8. Theintegrated combustor/reformer of claim 7 wherein the integratedcombustor/reformer is characterizable by a thermal efficiency such thatwhen H₂O and methanol in a 1.2:1 molar ratio are feed into the reformingchamber at a contact time of 1.0 seconds, and hydrogen and air in aH₂:O₂ ratio of 0.5 are combusted in the combustion chamber at a ratesufficient to obtain an average temperature of 320° C. within thereforming chamber, there is, at steady-state, a thermal efficiency of atleast 10%, and the product gas contains 0.50 mole % or less CO.
 9. Theintegrated combustor/reformer of claim 8 wherein the integratedcombustor/reformer is characterizable by a thermal efficiency such thatwhen H₂O an methanol in a 1.2:1 molar ratio are feed into the reformingchamber at a contact time of 1.0 seconds, and hydrogen and air in aH₂:O₂ ratio of 0.5 are combusted in the combustion chamber at a ratesufficient to obtain an average temperature of 320° C. within thereforming chamber, there is, at steady-state, a thermal efficiency inthe range of 10 to 35%, and the product gas contains 0.5% or less CO.10. The integrated combustor/reformer of claim 8 wherein the integratedcombustor/reformer is characterizable by a thermal efficiency such thatwhen H₂O and methanol in a 1.2:1 molar ratio are feed into the reformingchamber at a contact time of 1.0 seconds, and hydrogen and air in aH₂:O₂ ratio of 0.5 are combusted in the combustion chamber at a ratesufficient to obtain an average temperature of 320° C. within thereforming chamber, there is, at steady-state, a thermal efficiency inthe range of 10 to 25%, and the product gas comprises H₂ in a H₂:COratio of 10,000:1 or less.
 11. The integrated combustor/reformer ofclaim 8 having a volume of 20 ml or less and does not contain repeatingunits.
 12. The integrated combustor/reformer of claim 7 that ischaracterizable by a thermal efficiency such that when H₂O and methanolin a 1.2:1 molar ratio are feed into the reforming chamber at a contacttime of 1.5 seconds, and fuel and oxygen are combusted in the combustionchamber at a rate sufficient to obtain an average temperature of 320° C.within the reforming chamber, there is, at steady-state, a thermalefficiency of at least 10%, and the product gas contains 0.1 mole % orless CO.
 13. The integrated combustor/reformer of claim 10 wherein thereforming chamber is a channel having at least one dimension of 5 mm orless and wherein the reforming chamber comprises a methanation catalyst.14. The integrated combustor of claim 1 wherein the endothermic reactionchamber comprises a channel length that is at least 4 times greater thanchannel height or width.
 15. The integrated combustor of claim 1 whereinthe endothermic reaction chamber comprises a steam reforming catalystcomprising Pd.
 16. The integrated combustor/reformer of claim 7 whereinthe reforming catalyst comprises Pd on ZnO and has a Pd:Zn molar ratioof 0.1 to 0.8.
 17. The integrated combustor/reformer of claim 7 whereinthe reforming catalyst is characterizable as having a methanolconversion of at least 70% and a CO selectivity of 2% or less at 260° C.18. The integrated combustor/reformer of claim 7 wherein the reformingcatalyst comprises Pd on ZnO and has a Pd:Zn molar ratio of 0.2 to 0.5.19. The integrated combustor of claim 1 wherein the endothermic reactionchamber comprises a reforming zone, a water-gas shift zone and amethanation zone; wherein the reforming zone is nearest the combustionchamber, the water-gas shift zone is next nearest the combustion, andmethanation zone is furthest from the combustion chamber.